The objective of this project is to develop an efficient and accurate system for monitoring the movements of the human mandible in real time. The system will find application in several areas of dental practice. It will be used to measure and display the functional movements during speaking and chewing, and to store a record of those movements. Because a detailed mathematical record is stored, the system will be able to be used to determine functional change after dental restoration, treatment of TMJ dysfunction, orthognathic surgery, or orthodontic treatment. The system consists of a personal computer-based control unit, a non-restraining extra-oral harness to which is attached a set of LED's, and two detectors to track the LED's in space. The prototype system developed under Phase I can track 8 LED's at a rate of 32 cycles per second. Data are displayed as they are collected, and stored for later analysis. Initial Phase I clinical investigation has indicated that the system is non-constraining, simple to operate, and can collect and display data of clinical interest. Technical work in Phase II will concentrate on improving system accuracy, adding three dimensional graphics capabilities, and improving the harness design. Larger clinical investigations will be conducted in a number of dental disciplines in order to explore the range of clinical utility of the system.